Telephone system



INVENTOR.

ElarEnceELumax MW, MM ATTORNEYS C. E. LOMAX TELEPHONE SYSTEM Filed July 20, 1938 2 Sheets-Sheet 1 mwzwmuxm 3 Jan. 23, 1940.

Jan. 23, 1940- c. E. LoMAx TELEPHONE SYSTEM Filed July 20, 1938 2 Sheets-Sheet 2 INVENTOK Clarence E. Lumax m MM ATTORNEYS Patented Jan. 23, 1940 UNITED STATES PATENT 4 OFFICE Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application July 20, 1938, Serial No. 220,162

18 Claims.

. The present invention relates to telephone systems and more particularly to improvements in intercommunication telephone systems of the character adapted for use in conjunction with 5 the apparatus of a regular telephone system.

In an intercommunication telephone system designed to provide more direct communication facilities between one or more master or executive telephone stations and a plurality of subordinate telephone systems, direct lines are usually provided" which individually extend between the master stations and the subordinate stations. For the convenience of the subscriber in whose oflice a master station is located, it is desirable to provide thereat an auxiliary'transmitter and an auxiliary receiver in the form of a loud speaker. The provision of such auxiliary transmitting and receiving elements gives rise to the problem of obtaining a sufliciently high level of sound output from the loud speaker and a sufiiciently high sound input to the auxiliary transmitter to render a conversation bein held over one of the direct lines readily understandable at each end of the line. In the past it has been the practice tosolve this problem by using one or more vacuum tube amplifiers for raising the level of the signal currents transmitted from and received at the master station, thereby to insure the requisite sound output levels at each end of the connection extending to the master station. While this arrangement is perfectly satisfactory in operation, it is somewhat expensive and, accordingly, it is desirable to avoid the use of amplifiers wherever possible. It is an object ofthe present invention to provide an improved telephone system of the character described wherein the circuit apparatus is arranged in an improved manner to minimize all signal energy losses in the signal current transmission channel, whereby no amplification is required for satisfactory sound reproduction when auxiliary transmitting and receiving units are provided at the master station.

It is another object of the invention to provide, in a system of the character described, an improved substation circuit which may selectively be connected to either of two lines ex tending to the circuit and is so arranged that the induction coil included therein is only operatively connected in the circuit when the circuit is connected to a particular one of the two lines extending thereto. It is a further object of the invention to provide, in a system of the character described, improved circuits for signaling between the stations of the system, which circuits are so arranged that the identity of calling stations is indicated at the called stations.

The invention is illustrated as being embodied in a telephone system wherein the lines iorming the intercommunication network are provided as an adjunct. to the regular substation lines and the switching apparatus of an automatic exchange by way of which connections are established between the regular substation lines in the usual manner. The arrangement of the apparatus is such that the subordinate substation circuits and, more particularly, the transmitters and receivers respectively embodied therein are used both on regular calls routed by way of the automatic exchange and on calls routed by way of the subordinate or direct lines forming the intercommunication network. In the illustrated embodiment of the invention there are provided a plurality of master or executive telephone stations and a plurality of subordinate telephone stations, together with lines directly extending between each of the master stations and each of the subordinate stations. In accordance with one feature of the invention, each of the master stations includes signal devices individually corresponding to the subordinate stations, which signal devices form a part I of means for identifying calling ones of the subordinate stations on direct calls incoming to the master stations. Also, signal devices individually corresponding to the master stations are provided at each of the subordinate stations, these latter signaling devices forming a part of means for identifying calling ones of the master stations on calls incoming to the subordinate stations. In accordance with a further feature of the invention, the switching apparatus which is operative to set up a direct call connection between any one of the master stations and any one of the subordinate stations includes means for excluding the induction coil or coupling device from the substation circuit of the subordinate station, thereby to minimize the signal energy losses involved in the connection to an extent such that an auxiliary transmitter and auxiliary receiving means of the loud speaking type may satisfactorily be used at the master station without providing any amplification in the signal current transmission channel. More particularly, the lines making up the intercommunication network are provided with three conductors each, and the switching apparatus utilized in setting up a direct call connection between one of the master stations and one of the-subordinate stations includes a switch located at the subordinate station which is operative to couple the receiver at the subordinate station to one pair of conductors of the line extending to the master station, and also to connect the transmitter at the subordinate station directly to another pair of conductors of the line extending to the master station, whereby the induction coil of the subordinate substation circuit is excluded from this circuit and substantially independent channels are provided for transmitting audio frequency energy between the connected stations in the respective two directions of transmission.

Further features of the invention pertain to the particular arrangement of the circuit elements whereby the above and additional operating features are attained.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of op eration, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figures 1 and 2, taken together, illustrate a telephone system having embodied therein the features of the invention as briefly outlined above.

Referring now to the drawings, the system there illustrated comprises an automatic exchange It having line switching apparatus embodied therein which may be of any desired construction and arrangement, although preferably this apparatus is of the well-known Strowger step-by-step automatic type. For example, the switching apparatus provided in the exchange l0 may conventionally comprise non-numerical finder switches of the Strowger type having access to the various lines of the system, impulse responsive trunk selecting selector switches individually associated with the finder switches,

A and impulse responsive connector switches, also of the Strowger type, accessible to the selector 5 switches and having access to the lines of the system. Extending to the exchange in and terminating in the bank contacts of the various finder and connector switches are a plurality of substation lines, four of which are indicated at H, l2, l3 and M, respectively. The lines H and I2 individually extend to the telephone stations A and B which are of identical arrangement and are designated as being master or executive stations. The lines l3 and I 4, on the 5 other hand, individually extend to the substations l5 and [6 which are also of identical arrangement and are hereinafter referred to as subordinate stations.

Briefly described, the apparatus provided at the master station A comprises a transmitter l1 and a receiver l8 which are preferably combined to form an instrument of the hand-set type. This instrument, when not in use, is supported upon a cradle or hook, not shown, but is removable therefrom for use. Arranged to operate in response to removal of the hand-set from its supporting element is a hook switch l9 which comprises the switch springs indicated at 20 to 23, inclusive. The substation apparatus provided at the station A further comprises a signal device in the form of a bell or ringer 29 bridged between the line conductors a and b of the line H in series with a condenser 30. This signal device is arranged to be energized in response to the application of ringing voltage to the line II when this line is seized by one of the connector switches in the exchange l0 and is found to be idle. For the purpose of controlling the automatic switching apparatus provided in the exchange III on regular calls outgoing from the stationA, there is provided an impulsing device 24 which comprises impulsing springs 25 and shunt springs 26, 21 and 28. The transmitter ll, the receiver l8, the hook switch I9 and the impulsing device 24 are interconnected-with the win i g 32.33

and 36 of an induction coil 3| to form a. substation circuit of the well-known anti-side-tone type.

The apparatus provided at the master station A and thus far described is normally used on calls routed by way of the line H extending to the automatic exchange I 0. There is also provided at this telephone station apparatus which is adapted to be used on calls routed by way of the lines of the intercommunication network and referred to more particularly hereinafter. This additional apparatus comprises an auxiliary transmitter 35, auxiliary receiving means in the form of a loud speaker 36 and an induction coil 49 which comprises the windings indicated at 50 to 51, inclusive. For the purpose of initiating and answering calls routed by way of the lines directly extending to the subordinate telephone stations, there are provided a plurality of key operated call and answer switches ll, 1'5, etc., which individually correspond to the subordinate telephone stations. Each of the call and answer switches H, Ha, etc., is of the locking type such that when once operated to its off-normal position it is restrained in its oilnormal position until manually restored to normal. In order to identify the calls incoming to the master station A and routed by way of the lines of the intercommunication network, there are provided a plurality of visual signal devices comprising the drops 63, 633., etc., which also individually correspond to the subordinate stations and are only operative on calls incoming from the respective corresponding subordinate stations. The visual signals afl'orded by the selective operation of the drops 63, 63a, etc., are supplemented by an audible signal which is pro duced by operation of a buzzer 62 commonly associated with all of the subordinate stations. For the purpose of controlling the buzzer 62 and for additional control purposes described in greater detail hereinafter, there are provided four relays Rlllll, RI l0, RIM and RI20, the last of which is of the slow-to-operate type and is in effect a slow acting device operative in response to operation of the relay Rl30. particularly, the relay R is commonly included in the operating circuits for all of the drops 63, 63a, etc., and is operative to initiate the operation of the buzzer 62. The relay Rl2ll is also operative in response to operation of the relay Rl3ll and is arranged to arrest the operation of the buzzer 62 when it assumes its fully operated position. The two relays RIIIO and RI! cooperate to cause the operation of the buzzer 62 when a conversing party at the telephone station A neglects to restore an operated one of the switches ll, Ha, etc., to normal after the connection has been cleared out at the end distant from the station A. A key controlled switch comprising the contact springs 9 is provided for controlling the relay Ri3ll in the manner described indetail hereinafter. For the purpose of transmitting ringing current by way of a selected one of the subordinate lines, there is provided a key operated ringing switch 64 which is of the non-locking type and includes contact springs 65 and 10 connected to the opposite terminals of a ringing current source, not shown.

As indicated above, the transmitter l1 and the receiver l8 are normally used in conjunction with calls routed by way of the regular substation line H, and the auxiliary transmitter 35 and loud speaker 36 are normally used on calls routed by way of the lines of the intercom'munication network. The arrangement is such, however, that thetransmitter l1 and the receiver l8 may be used on calls of the latter character. To this end a key operated transfer switch 31 of the locking type is provided which includes contact springs appropriately arranged to permit the transmitter l1 and the receiver 18 to be substituted for the auxiliary transmitting and receiving means, respectively, in communicating over any established connection utilizing one of the lines of the intercommunicatlon network.

In the arrangement illustrated, only four of the subordinate lines making up the intercommunication network are illustrated, which four lines are indicated at 82, 83, 84 and 85, respectively. Of the enumerated lines, the line 82 extends between the master station A and the subordinate station l5; the line 83 extends between the master station B and the subordinate station IS; the line 84 extends between the master station A and the subordinate station l6; and the line 85 extends between the master station B and the subordinate station IS.

The subordinate stations include the same apparatus arranged in the same manner and, hence, only the details of the subordinate station [5 are illustrated. In brief, the apparatus provided at this station comprises a transmitter 86, a receiver 81 and an induction coil 9| arranged to be interconnected to form a substation circuit of the wellknown anti-side-tone type. The substation circuit includes one set of line terminals for each line incoming thereto. Thus, the conductors of the line l3 are connected to the line terminals 6a and 6b; the three conductors of the line 83 are connected to the line terminals 1a, 1b and 1c; and the three conductors of the line 82 extend to the line terminals 8a, 8b and 8c. The transmitter 86 and the receiver 81 are preferably combined to form an instrument of the hand-set type which is supported upon a cradle when not being used and is removed therefrom when taken for use. Arranged to be operated in response to removal of the receiver 81 from its supporting cradle is a cradle or switch hook 88 comprising contact springs 224 to 221, inclusive, shown in the closed circuited position which they assume when the receiver is removed from its supporting element. The apparatus provided at the station l5 further comprises a signal device in the form of a ringer s bridged between the line conductors Be and I31, of the line 13 in series with a condenser 96a. This signal device is only operative on calls routed by way of the automatic switching equipment provided in the exchange I8 and when ringing current is projected by this apparatus over the line l3.

In order to adapt the transmitting and receiving means provided at the station I5 for use on calls routed from the master stations over the subordinate lines to the station [5, there is provided a pair of switching relays R208 and R2") which individually correspond to the master stations A and B, respectively. The relay R20ll is arranged to be controlled by a key operated switch comprising the springs 91, and the relay R2 I8 is provided with an operating circuit which is similarly arranged to be completed through operation of a key controlled switch comprising the springs 98. The two key operated switches noted are of the locking type and each thereof is operable to its off-normal position to close the contact springs embodied therein without afiecting the position of the other switch. A mechanical interlock indicated by the dotted line U is provided between the operating mechanism of each of the two key controlled-switches and the operating mechanism of the hook or cradle switch 88. This mechanical interlock is so arranged that either of the two key controlled switches may be operated to the oil-normal position without aifecting the position of the cradle or hook switch 88 but, when the receiver 81 is replaced upon its supporting element, any operated one of the two key controlled switches is restored to its normal position. Since key controlled switches arranged partially to be controlled by an associated hook switch in the manner just described are well known in the art, the details of the mechanical arrangement are omitted in the interests of simplii'ying the disclosure. For the purpose of signaling the subordinate station subscriber on calls incoming to the station 15 and routed by way of the subordinate lines 82 and 83, there are provided two additional signal devices in the form of ringers 95b and 95 which individually correspond to the master stations B and A, respectively. More particularly, the ringer 95b is bridged between the line conductors 83a and 83b in series with a condenser 96b, and the ringer 95c is bridged between the line conductors 82a and 82b in series with a condenser 96c. The plurality of signal devices 95a, 95b and 95 individually have distinctive tone characteristics such that the produced tone occasioned by operation of any one thereof indiizates the particular master station which is call- The manner in which calls are routed by way of the automatic switching equipment provided in the exchange l8 between the various substations of the system is, in all respects, substantially similar to the operation of any conventional automatic system. Briefly, to consider the operation of the apparatus to set up a connection between the stations A and IS on a call initiated at the master station A, it is pointed out that operation of the apparatus is initiated when the calling party removes the receiver l 8 from its supporting element to cause the contact springs of the hook or cradle switch 19 to be moved to the closed circuited position illustrated in the drawings. It will be noted that with the switch I!) in this position, a direct current bridge is placed across the line conductors of the line I I individual to the master station A. The bridging path may be traced as extending by way of the conductor I la, the springs 4|, 40 and 25, the transmitter H, the springs 44. 43, 23 and 22 and the induction coil winding 33 to the opposite line conductor llb. When this bridging path is completed, a selected one of the non-numerical finder switches provided in the exchange I8 is caused to operate to seize the calling line H and to switch the calling loop circuit through to an associated one of the numerical selector switches. When this operation is completed, dial tone is returned over the loop to indicate to the calling party that the dialing operation may be started. During the dialing operation, the calling loop circuit is interrupted at the springs 25 of the impulsing device 24 a number of times determined by the directory number identifying the called subordinate station l5 Also, during each series of impulses, the shunt springs 28, 21 and 28 are moved to the closed circuited position to short-circuit the transmitter l1 and the receiver l8 in the usual manner. The seized selector switch in the exchange I 8 responds to the impulses of the first digit dialed at the master station A by selecting an idle one of the group of connector switches having access to the lines each time one of the connector switches is operated to a position corresponding to a desired called line. Thus, in the case here being considered, when the line I3 is selected by an operated one of the connector switches in the exchange In, this switch operates to determine the idle or busy condition of the line l3. If the line is busy at the time it is selected, busy tone current is returned over the calling loop circuit and the resulting operation of the receiver I8 indicates to the calling party that the desired connect on cannot immediately be obtained. On the other hand, if the called line is idle at the time it is selected, ringing current is projected over the line l3 to energize the signal device 95a and ring-back-tone current is projected back over the calling loop circuit to indicate to the calling party that the ringing operation is being performed.

The desired conversational connection is completed when the call is answered at the subordinate station [5. More particularly, when the answering party removes the hand-set comprising the receiver 81 from its supporting cradle, the switch 88 is operated to its off-normal position so that the springs 224 to 221, inclusive, assume the closed circuited positions indicated in the drawing. It will be noted that, with the switch 88 occupying its ofi-normal position, a direct current bridge is placed across the line conductors I35 and I31 of the line Hi. This bridging path may partially be traced as extending by way of the conductor I38, RC2I2, RAZI I, RC202, RA20I, the impulsing springs 223, the transmitter 86, RA2I4, RC2l5, RA204, R0206, the springs 22! and 226, and the induction coil winding 93 to the opposite line conductor l3. When this bridging path is completed, certain of the control apparatus embodied in the selected connector switch in'the exchange I is caused to operate to arrest the ringing operation and to reverse battery back over the calling loop circuit to the calling station A; The manner in which the release of the established connection is achieved depends upon the character and arrangement of the automatic switching equipment provided in the exchange I 0. For example, this equipment may be so arranged that the release of the operated switch train is only efiected when the connection is cleared out at both ends thereof. Alternatively, the switching equipment may be so arranged that the release of the connection is under the control 'of the calling party. In any case, the operated switch train is released when the calling and called parties hang up to interrupt the respective bridging paths traced previously. Obviously, when the handsets respectively provided at the stations A and I are replaced upon their respective supporting cradles, the two hook or cradle switches l9 and 88 are respectively returned to their normal positions and the substation apparatus located at each of the two stations A and I5 is returned to normal. 4

The manner in which a connection is routed from the subordinate station l5 by way of the automatic switching equipment. provided in the exchange I0, to the master station A, is substantially similar to the operation of the apparatus as described above. In this case, the impulsing decalled line l3. "The selector connector switch, in

vice 88 is utilized to transmit the switch control impulses to the automatic switching equipment provided in the exchange l0, and the signal device 29 provided at the station A is energized during the ringing operation. Aside from these two differences the connection is completed and released in the manner described above with reference to the call initiated at the station A;

From the foregoing description it will be apparent that on any call routed by way of the automatic exchange l0 to or from the subordinate station l5, the windings of the induction coil 9| are operatively included in the substation circuit provided at the station I 5. The purpose of including this induction coil is to eliminate the side tone in the usual manner. The induction coil 9| is incidentally effective to absorb a portion of the voice frequency energy transmitted to and from the subordinate station. When the usual type of receiver is being used at each end of the connection, this absorption of energy is of no importance since the level of signal energy transmitted from the station l5 to the other end of the connection is amply sufficient when the sound is being transmitted to the ear of a listener through a receiver held closely adjacent the listeners ear. When, however, a reproducing device of the loud speaking type is utilized at the distant end of the connection, the loss of energy occasioned by the inclusion of the induction coil 9| in the substation circuit of the station l5, or another similar station, is objectionable since it tends to lower the level of the sound output of the loud speaker. To obviate this difiiculty there is provided at each of the subordinate stations means comprising the switching relays R200 and R2! for excluding the induction coil 9| from the substation circuit on calls routed by way of the subordinate lines making up the intercommunication network.

Referring now more particularly to the operation of the apparatus on a call initiated at the subordinate station l5 and routed by way of the line 82 to the master station A, it is pointed out that to initiate the call the calling party first operates the key controlled switch comprising the springs 81 to the oil-normal position, thereby to complete an obvious circuit for energizing the relay R200. Upon operating, the relay R200 disconnects the substation apparatus from the line i3 and operatively associates this apparatus with the conductors of the line 82 extending to the master station A. More particularly, at RA20I and RA204 and their respective associated contacts RC203 and R0205, the relay R200 connects the transmitter86 across the line conductors 82a and 82b. At RAZM and RA20'I and their respective associated contacts RC205 and R0208, the relay R200 prepares a path for connecting the receiver 81 across the line conductors 82b and 82::- Following operation of the switch comprising springs 91 to the ofi-normal position to cause the operation of R200, the calling party removes the handset from its supporting cradle, thereby to cause the switch 88 to be operated to its off-nor-- RAM I the impulsing springs 223, the transmitter 82, RA2I4, RC2I5, RA204, R0205, the line conductor 82b, the springs 18 and 11, the winding of the drop 63 and the winding of RI30 to battery. When energized over this circuit, the drop 63 operates to give a visual indication that a call originating at the subordinate station I5 awaits attention. The relay RI30 also operates when energized over the circuit just traced and, upon operating, completes at RAI3I a circuit extending by way of RAI2I for energizing the buzzer 62. The resulting operation of the buzzer 62 informs the subscriber at the master station A that an incoming call awaits attention, and by observing the operated condition of the drop 63 the called subscriber is informed that the subordinate station I5 is the calling station. With theswitch springs 9 in the closed circuited position shown, operation ofthe signal device 62 is of limited duration since, upon operating, the relay RI30 completes, at RAI3 I, a circuit extending by way of the springs 9 for energizing the slow-to-operate relay RI20. The last-mentioned relay operates after an interval to open at RAI2I a point in the above-traced circuit for energizing the signal device 62, thereby to arrest the operation of this device.

The party who answers the call has the option of using the hand-set comprising the transmitter I1 and the receiver I8 or the auxiliary transmitter 35 and the auxiliary receiving means 36 in communicating over the connection. Assuming that the transmitter 35 and the receiver 36 are to be used, the call is answered by operating the call and answer switch 1|, corresponding to the station I5, to the off-normal position. When the switch H is operated to its oiT-normal position, two points are opened in the abovetraced circuit for energizing the winding of the drop 63 in series with the relay RI30, and a circuit is completed for energizing the relay RI in series with the transmitter 86 provided at the calling station I5. Upon restoring, the relay RI30 opens, at RAI3I, a further point in the circuit for energizing the buzzer 62 and a point in the operating circuit for R120, causing the last-mentioned relay to restore. The circuit for energizing RI00 and the transmitter I extends from ground at the upper terminal of the winding 51 by way of this winding, the springs 61, 66, 14 and 15, the line conductor 82a, RC203, RA20I, the impulsing springs 223, the transmitter 86, RA2I4, RC2I5, RA204, R0205, the line conductor 82b, the springs 18, 19, 69 and 68, the winding 56 and the winding of RI00 to battery. When energized over this circuit, the relay RI00 operates to interrupt at RAIOI and RCI02 a point in the operating circuit, traced hereinafter, for RIIO. It will be noted that talking battery voltage is impressed across the terminals of the transmitter 86 over the circuit just traced and by Way of which RI00 is energized. It will further be noted that the windings of the induction coil 9| are excluded from this circuit. At RAIOI and RCI03, the relay RI00, upon operating, completes a circuit for impressing talking battery voltage across the terminals of the transmitter 35. More particularly, the transmitter 35 is energized over a circuit extending from ground at RAIOI by way of RCI03, the winding 5|, the transmitter 35, the springs 38 and 39, the winding 50 and the resistor 50' to battery. Following the operation of the switch H to its ofinormal position, the desired communication connection is fully established. This connection comprises two substantially independent channels for transmitting audio frequency energy in the respective two directions of transmission. More particularly, voice frequency currents developed by operation of the transmitter 35 circulate in the closed circuit comprising this transmitter 35, the winding 5I, the condenser 59, the winding 50 and the switch springs 39 and 38. By virtue of the alternating character of these currents, corresponding induced voltages are developed in the coupled windings 54 and 55 o! the induction coil 49. These induced voltages cause corresponding currents to flow through the receiver 81 provided at the subordinate station I5, the closed circuit traversed by these currents extending from the lower terminal of the winding 55 by way of the springs 68, 69, 19 and 18, the line conductor 82, R0205, RA204, RC2I5, RA2I4, the receiver 81, the springs 224, RA201, R0208, the line conductor 82, the springs 8| and 80, the winding 54, the condenser 58 and the winding 55 back to the lower terminal of the last-named winding. The circuits just described constitute the channel for transmitting energy developed by operation of the transmitter 35 to the receiver 81. Voice frequency currents developed by operation of the transmitter 86 traverse a circuit which may be traced as extending from the lower terminal of the transmitter 86 by way of RA2I4, RC2I5, RA204, RC205, the line conductor 82b, the switch springs 18, 19, 69 and 68, the winding 56, the condenser 6|, the winding 51, the switch springs 61, 66, 14 and 15, the line conductor 82a, R0203, RA20I and the impulsing springs 223 to the upper terminal of the transmitter 86. Due to the alternating character of these currents, corresponding induced voltages are developed in the windings 52 and 53 coupled respectively to the windings 56 and 51. These induced voltages cause corresponding currents to traverse the closed circuit which comprises the windings 52 and 53, the condenser 60, the switch springs 41 and 48 and the voice coil of the loud speaker 36. The circuits just described constitute the other channel, namely, that for transmitting voice frequency energy from the subordinate station I5 to the master station A. It will be noted that the two channels have commonly included therein the line conductor 82b. The resistance of this conductor, however, is insufiicient to provide any substantial coupling between the two channels. Also, the induction coil 49 is so arranged that the windings 52, 53, 56 and 51 are well shielded from the windings 50, 5I, 54 and 55 so that no substantial coupling exists between the two sets of windings. Hence singing of the network is reduced to a minimum.

The key operated switch comprising the springs 9 is provided for the purpose of opening a point in the operating circuit for the slow-to-operate relay RI20, whereby the buzzer 62 is caused continuously to operate when a call is extended by way of one of the subordinate lines to the master station A and until the call is answered. Thus, in the case considered above, if the key operated switch comprising the springs 9 occupies its off -normal position, such that the springs 9 are open at the time the relay RI30 operates, the operating circuit for RI 20 is not completed in response to operation of the relay RI30 and, hence, the buzzer 62 is continuously energized over the circuit extending from ground at RAI3I until the call is answered at the master station A. When the call and answer switch H is operated to its ofi-normal position to answer the call, the operating circuit for Rl38 is interrupted and the last-mentioned relay restores to open, at R.A|3|, the operating circuit for the buzzer 82, thereby to terminate the signal. Thus, it will be seen that by providing the key controlled switch comprising the springs 8, the subscriber at the master station A has the option of arranging the circuit so that the buzzer 62 is energized for a limited time interval or is continuously energized on calls routed by way of the subordinate lines to his substation.

As indicated previously, the hand-set comprising the transmitter l1 and the receiver l8 may be used in lieu of the transmitter 35 and the loud speaker 38 in communicating over the connection just described. In order operatively to include the transmitter I1 and the receiver I8 in the substation circuit of the station A, the transparty in the station A neglects to restore the switch II to normal, a circuit is completed for energizing the buzzer 82 when the connection is cleared out at the station l5. More particularly, when the hand-set provided at the station I5 is replaced upon its supporting cradle to cause the restoration of R28fl, the loop circuit over which R100 is being held energized is interrupted at RA28I and RA204 and their respective associated contacts R0203 and R0205. Upon restoring, the relay RIM completes at RAIOI a circuit for energizing RI II), this circuit extending from ground at RAIOI by way of RCI02, the switch springs 13 and I2 and the winding of RIIO to battery. Upon operating, the relay RH 0 comfer switch 31 is operated t t ofl-normal s1-.- p'letes, at RAI l2, an obvious alternative circuit tion. Operation of this switch to its off-normal position effects a direct substitution of the transmitter II for the transmitter 35 and of the receiver l8 for the loud speaker 36 in the substation circuit. Thus, at the springs 43 and 46 and their respective'associ'ated springs 42 and 48, the receiver I8 is substituted for the loud speaker 38 in the substation circuit. At the springs 43 and and their respective associated contacts 42 and 38 the transmitter I1 is likewise substituted for the transmitter 35 in the substation circuit. Obviously, by operating the transfer switch 31 between its two operating positions, the hand-set may be substituted for the. auxiliary transmitting and receiving means at will and as many times as desired during a single conversation. By providing this feature, it is possible for the subscriber at the station A to use the regular handset when he desires to carry on a semi-private conversation with a party located at one of the subordinate stations.

In order to release the connection as established in the manner set forth above, the switch II is returned to its normal position and the hand-set comprising the transmitter 86 and the receiver 81 is replaced upon its supporting cradle. Also, if the hand-set comprising the transmitter I"! and the receiver I8 is being used at the station A, this hand-set is replaced upon its supporting cradle and the transfer switch 31 is returned to its normal position. When the switch II' is restored to its normal position, the two voice frequency energy transmission channels described above are interrupted and the operating circuit for the relay RIM is opened, thus completely breaking the connection. When the hand-set comprising the transmitter I1 and the receiver I8 is replaced upon its supporting cradle, the hook switch I9 is returned to its normal position and, thus, the apparatus provided at the station A is completely restored to normal. When the calling party at the station I5 replaces the hand-set upon its supporting cradle, the cradle switch 88 is restored to normal and, through operation of the mechanical interlock U, the key controlled switch comprising the springs 91 is also restored to its normal position. When the last-mentioned switch is restored to normal, the springs 91 are opened to interrupt the operating circuit for R208, causing this relay to restore to reconnect the substation circuit for use in communicating over the line l3. 7

As pointed out previously. provisions are made for energizing the buzzer 62, and the resulting operation of the buzzer gives an audible indication that the switch II should be returned to its normal position. When the switch II is thereafter restored to normal the operating circuit for BI ID, as traced'above, is interrupted at the springs 12 and 13, causing this relay to restore to open at RA|I2 the operating circuit for the buzzer 62, thereby to terminate the signal.

In the event the call initiated at the subordinate station I5 is intended for the master station B rather than the master station A, the key operated switch comprising the springs 88 is operated by the calling party rather than the key operated switch comprising the springs 91. When the springs 98 are closed the relay R2! operates to connect the sub-station apparatus provided at the station ii to the line 83 extending to the master station B. Thus, at RAZI I and RA2|4 and their respective associated contacts RC2I3 and R0218, the relay R2l0, upon operating, connects the transmitter 86 across the line conductors 83a and 881.. Similarly, at RA2 l4 and RAM! and their respective associated contacts RC2I6 and RC2I8, the relay R2I0 prepares a path for connecting the receiver 81 across the line conductors 83b and 83:: of the line 83 extending to the master station B, which path is completed at the springs 224 of the switch 88 whenthe handset comprising the receiver 81 is removed from its supporting cradle. Aside from the fact that the switch comprising the springs 98 and the relay R2"! are operated, rather than the switch comprising the springs 91 and the relay R280, the mode of operation of the apparatus to establish a communication connection between the stations I5 and B is identical with that described above with reference to the connection set up between the stations l5 and A.

Referring now more particularly to the operation of the apparatus .to establish a connection including the line 82 and extending between the stations A and IS on a call initiated at the station A, it is pointed out that to initiate the call the switch H corresponding to the station I5 is first operated to its elf-normal position, at which time the above-traced circuit is completed for energizing RI l0. Upon operating, the relay Rllll completes, at RAII2, the above-described circuit for energizing the buzzer 82, but the resulting operation of the buzzer is without effect since the calling party is aware that its operation results from the initiation of the call. At RAII I,

the relay EHO, upon operating, applies ground to the ringing apparatus start conductor ill, thereby to initiate the operation of. this apparatus in the usual manner. Following operation of the switch H the ringing switch 64 is operated to its off-normal position one or more times to cause ringing current to be projected over the line 82 to the subordinate station l5. More particularly, when the ringing key 64 is operated to its off-normal position, the signal device 95 is energized over a circuit extending from one terminal of the ringing current source, not

I shown, by way of the springs 65, 56, 14 and 15,

the line conductor 82s, the condenser 969., the windings oi the signal device 95a, the line conductor 82b and the springs 18, 19, 69 and 10 to the opposite terminal of the ringing current source. The resulting operation of the signal device 95s indicates to the subscriber at the station l5 that his substation is being called from the master station A. To answer the call, the' subscriber at the subordinate station Ii'rfirst operates the key controlled switch comprising the springs 91 to its oif-normal position and then removes the hand-set comprising the receiver 81 from its supporting cradle to cause the switch 88 to operate to its off-normal position. At the springs 91 the above-traced operating circuit for R200 is completed. Upon operating, the relay R200 connects the transmitter 86 across the line conductors 82a and 82b, and the receiver 81 across the line conductors 82b and 82, all in the manner described previously. When the transmitter 86 is connected across the line conductors 82a and 82b, the above-traced circuit is completed for energizing the relay RIM which relay, upon operating, interruptsat RAIOI and RC |02, the previously traced operating circuit for Bill). Upon restoring, the relay Rll0 removes, at RAI I l, ground from the ringing apparatus start conductor Ill and opens, at RAHZ, the alternative operating circuit for the buzzer 62. With the cradle switch 88 and the relay R200 operated, the desired communication connection is fully established between the calling and called stations. This communication connection comprises the two substantially independent energy transmission channels described previously for transmitting voice frequency currents in the respective two directions of transmission. The manner in which the connection is released is the same as described previously and, hence, need not be repeated.

If a call intended for the subordinate station I 5 is initiated at the master station B, the manner in which the apparatus functions to set up the desired connection is in all respects, similar to the operation of the apparatus to establish a connection between the master station A and the subordinate station 15, it being pointed out, however, that when ringing current is projected over the line 83 to the subordinate station IS the signal device 95b is energized rather than the signal devices 953. and 950. Due to the distinctive tone of each of the three devicesnoted, the subscriber at the subordinate station I5 is able to discriminate between the signals and to ascertain from the particular tone produced by operation of any one of the signal devices the particular type of call, and also, which of the key controlled switches should be operated to answer the call. In a similar manner the subscriber located at the master station A is informed by the selective operation of the signal devices 63, 63a, etc., as to which of the call and answer keys such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a telephone system, an exchange includ-.

ing line switching apparatus, a first telephone station including a transmitter, a receiver and an audio frequency current coupling device arranged to be interconnected to form a substation circuit, a second telephone station, means comprising said line switching apparatus for setting up a connection between said stations which includes said substation circuit, switching means operative to exclude said coupling device from said substation circuit,-a line extending between said stations, and means comprising said line and said switching means for setting up an alternative connection between said stations which includes said substation circuit with said coupling device excluded therefrom.

2. In a telephone system, an exchange including' line switching apparatus, a first telephone station including a transmitter, a receiver and an induction coil arranged to be interconnected to form a substation circuit, a second telephone station, means comprising said line switching apparatus for setting -up a connection between said stations which includes said substation circuit, switching means operative to exclude said induction coil from said substation circuit, a line extending between said stations, and means comprising saidline and said switching means for setting up an alternative connection between said stations which includes said substation circuit with said induction coil excluded therefrom.

3. In a telephone system, an exchange including line switching apparatus, a first telephone station including a transmitter, a receiver and an induction coil arranged to be interconnected to form a substation circuit, a second telephone station, means comprising said line switching apparatus for setting up a connection between said stations which includes said substation circuit, switching means operative to exclude said induction coil from said substation circuit, a multi-conductor line extending between said stations, and means comprising said line and said switching means for setting up an alternative connection between said stations which includes separate and substantially independent channels for transmitting audio frequency energy between said stations in the respective two directions of transmission, said alternative connection including said substation circuit with said induction coil excluded therefrom.

4. In a telephone system, an exchange includinduction coil arranged to be interconnected to form a substation circuit, a second telephone station, means comprising said line switching apparatus for setting up a connection between said stations which includes said substation circuit, switching means operative to exclude said induction coil from said substation circuit, a line extending between said stations and comprising a common conductor and two additional conductors, and means comprising said line and said switching means for setting up an alternative connection between said stations, said switching means comprising a switch located at said first station and operative to couple said receiver to said common conductor and one of said additional conductors and to connect said transmitter directly to said common conductor and the other of said additional conductors, whereby said induction coil is excluded from said circuit and substantially independent channels are provided for transmitting audio frequency energy between said stations in the respective two directions of transmission.

6. In a telephone system, an exchange including line switching apparatus, a first telephone station including a transmitter, a receiver, and an induction coil arranged to be interconnected to form a substation circuit, a second telephone station, means comprising said line switching apparatus for setting up a connection between said stations which includes said substation circuit, switching means operative to exclude said induction coil from said substation circuit, a line extending between said stations and comprising a common conductor and two additional conductors, and means comprising said line and said switching means for setting up an alternative connection between said stations, said switching means comprising a switch located at said first station and operative to couple said receiver to said common conductor and one of said additional conductors and to connect said transmitter directly to said common conductor and the other of said additional conductors, whereby said induction coil is excluded from said circuit and substantially independent channels are provided for transmitting audio frequency energy between said stations in the respective two directions of transmission, said switching means further comprising a second switch located at said second station and operative to impress talking battery voltage between said common conductor and the other of said additional conductors, thereby to energize said transmitter.

'7. A telephone station including a transmitter, a receiver and an induction coil arranged to be interconnected to form a substation circuit, said circuit including two sets of line terminals adapted to be connected to two different lines extending to said station, means operative to connect said transmitter and receiver for use II. in communication over the line extending to one of said two sets of terminals. and means operative to connect said transmitter and receiver for use in communication over the line extending to the other set of terminals and for excluding said induction coil from said circuit.

8. A telephone station including a transmitter, a receiver and an induction coil arranged to be interconnected to form a substation circuit, said circuit including a pairof line terminals adapted to be connected to the conductors of a two conductor line extending to said station, said circuit also including a set of three line terminals adapted to be connected to the conductors of a three conductor line extending to said station, means operative to arrange said circuit for use in communicating over the line extending to said pair of terminals, and means operative to connect said transmitter for use in communicating over a pair of the conductors of said three conductor line and to connect said receiver for use in communicating over a different pair 01 the conductors of said three conductor line.

9. A telephone station including a transmitter, a receiver and an induction coil arranged to be interconnected to iorm a substation circuit, said circuit including a pair of line terminals adapted to be connected to the conductors of a two conductor line extending to said station, said circuit also including a set of three line terminals adapted to be connected to the conductors of a three conductor line extending to said station, means operative to arrange said circuit for use in communicating over the line extending to said pair of terminals, means operative to connect said transmitter for use in communicating over a pair of the conductors or said three conductor line and to connect said receiver for use in communicating over a diiferent pair of the conductors of said three conductor line, said last-named means including switching means for excluding said induction coil from said circuit.

10. A telephone station including a transmitter, a receiver and an induction coil arranged to be interconnected to form a substation circuit, said circuit including a pair of line terminals adapted to be connected to the conductors of a two-conductor line extending to said station, said circuit also including two sets of three line terminals, each of said two sets of terminals being adapted to terminate a three conductor line, means operative to arrange said circuit for use in communicating over the line extending to said pair of terminals, and means operative selectively to connect said transmitter for use in communicating over a pair of the conductors of one of said three conductor lines and to connect said receiver for use in communicating over a cliiferent pair of the conductors of said one three conductor line.

11. A telephone station including a transmitter, a receiver and an induction coil arranged to be interconnected to form a substation circuit, said circuit including two sets of line terminals adapted to be connected to two diiferent lines, a supporting element for said receiver, means operative in response to removal of said receiver from said supporting element for connecting said transmitter and receiver for use in communicating over the line extending to one of said two sets of terminals, and means operative to connect said transmitter and receiver for use in communicating over the line extending to the other set of terminals and for excluding said induction coil from said circuit.

12. A telephone station including a transmitter,

a receiver and an induction coil arranged to be interconnected to form a substation circuit, said circuit including two sets. of line terminals adapted to be connected to two different lines, a supporting element for said receiver, means operative in response to removal of said receiver from said supporting element for arranging said circuit for use in communicating over the line extending to one of said two sets of terminals, a manually operable switch having a normal position and operable to an ofi-normal position, means operative in response to operation of said switch to said ofi-normal position for arranging said circuit for use in communicating over the line extending to the other set of terminals and for excluding said induction coil from said circuit, and means operative in response to replacement of said receiver on its supporting element for restoring said switch to its normal position.

13. A telephone station including a transmitter, a receiver and an induction coil arranged to be interconnected to form a substation circuit, said circuit including a pair of line terminals adapted to be connected to the conductors of a two conductor line extending to said station, said circuit also including a set of three line terminals adapted to be connected to the conductors of a three conductor line, a supporting element for said receiver, means operative in response to removal of said receiver from said supporting means for arranging said circuit for use in communicating over said two conductor line, and means operative to connect said transmitter for use in communicating over a pair of the conductors of said three conductor line and to connect said receiver for use in communicating over a different pair of the conductors oi! said three conductor line, said last-named means including switching means for excluding said induction coil from said circuit.

14. A telephone station including a transmitter, a receiver and an induction coil arranged to be interconnected to form a substation circuit, said circuit including a pair 01 line terminals adapted to be connected to the conductors of a two conductor line extending to said station, said circuit also including a set of three line terminals adapted to be connected to the conductors of a three conductor line, a supporting element for said receiver, means operative in response to removal of said receiver from said supporting means for arranging said circuit for use in communicating over said two conductor line, a manually operable switch having a normal position and operable to an ofi n'ormal position, means operative in response to operation of said switch for connecting said transmitter for use in communicating over a pair of the conductors of said three conductor line and for connecting said receiver for use in communicating over a diflerent pair of the conductors of said three conductor line, means also operative in response to operation of said switch to said oil-normal position for excluding said induction coil from said circuit, and means operative in response to replacement of said receiver on its supporting element for restoring said switch to normal.

15. In a telephone system, a plurality of master telephone stations, a plurality of subordinate telephone stations, lines extending between each of said master stations and each of said subordinate stations, means including said lines for setting up connections between said master stations and said subordinate stations, each of said master stations including signal de ices individually corresponding to said subordinate stations and arranged to be energized by way of the associated ones of said lines, means including said signal devices for identifying calling ones of said subordinate stations on calls incoming to the master stations, each of said subordinate stations including signal devices individually corresponding to said master stations and arranged to be energized by way of the lines extending to the corresponding master stations, and means including said lastnamed signal devices for identifying calling ones oi said master stations on calls incoming to said subordinate stations.

16. In a telephone system, a first telephone station, a plurality of telephone stations, lines extending from said first station to each of said additional stations, visual signal devices at said first station individually corresponding to said additional stations, a relay including a winding, each of said signal devices having an operating circuit, said operating circuits commonly including said Winding Whereby said relay is energized and operates when any one of said circuits is completed; each of said additional stations including a receiver and a manually operable switch; means individually provided at said additional stations and individually operative in response to operation of the corresponding switches for completing the operating circuits for the corresponding ones of said signal devices, and means operative in response to operation of said relay for giving an audible signal that said first station is being called.

17. In a telephone system, a first telephone station, a plurality of telephone stations, lines extending from said first station to each of said additional stations, visual signal devices at said first station individually corresponding to said additional stations, a relay-including a winding, each of said signal devices having an operating circuit; said operating circuits commonly including said winding, whereby said relay is energized and operates when any one of said circuits is completed; each of said additional stations including a receiver and a manually operable switch; means individually provided at said additional stations and individually operative in response to operation of the corresponding switches for completing the operating circuits for the corresponding ones of said signal devices, means operative in response to operation of said relay for giving an audible signal that said first station is being called, and a slow-acting control device operative in response to operation of said relay to terminate said audible signal.

18. In a telephone system, a first telephone station, a second'telephone station, a line extending between said stations, a signal device at said first telephone station, an operating circuit for said signal device; said second station including a transmitter, a receiver, a receiver supporting element and a manually operable switch; means controlled by operation of said switch and removal 01' said receiver from its supporting element for completing said operating circuit and for connecting said transmitter and receiver for use in communicating over said line, a switch at said first station, and means including said lastnamed switch for impressing talking battery voltage on said line, thereby to energize said transmitter only when said last-named switch is operated.

CLARENCE E. LOMAX. 

